Typical movie films are recorded at 24 Hz, 25 Hz or 30 Hz. Picture rates of common video cameras are 50 Hz and 60 Hz. Commercially available television displays, on the other hand, have picture rates up to 120 Hz, and employ either progressive or interlaced scanning. Hence, to interface broadcast video with a high-end TV display, the original sequence from the broadcast video needs to be up-converted using, for example, a picture rate converter. A picture rate converter typically operates by interpolating image frames at time instances where the frame sequence from a lower-frequency source device has yet to be registered in a higher-frequency destination display.
In simple picture rate converters, a picture is often repeated in the destination display until the next picture arrives from the source device, which often times results in blur and judder when motion occurs. Motion estimation and compensation circuits may be used in a picture rate converter to reduce these unwanted effects and achieve a high performance conversion for moving sequences. Motion compensation operates by estimating where elements of an interpolated picture would be, based on the direction and speed of the movement of those elements. The direction and speed values may then be expressed as motion vectors and are used to “move” the elements to the correct position in the newly interpolated frame. If this technique is applied correctly, its impact may be immediately visible on any picture sequence involving motion, where the resulting pictures can hardly be distinguished from the original sequences before the up-conversion.
It is thus desirable to determine methods and systems that minimize computational cost associated with motion-compensated picture rate conversion while maximizing its estimation accuracy. For example, various motion compensation schemes may be designed and applied to different regions within a sequence of source frames in order to achieve a balance between motion compensation efficiency and accuracy in the resulting interpolated frames. Also, motion compensation schemes themselves may be individually optimized to realize this balance of efficiency and accuracy. In addition, the entire system architecture of a motion-compensated picture rate converter may be designed to enhance its versatility in application and usage by making the architecture compatible with various display devices.